Atherosclerosis, in which a vessel gets partially or fully blocked by atheroma, is a common disease in the western world. Because of this there is a large research activity for developing catheter methods to remove the atheroma or expand the lumen of the artery. In laboratory experiments it has been possible to obtain ablation of the atheroma using laser light. This gives hopes for a method that can remove the atheroma even when there is only a thin hole left or full blocking of the artery.
A critical problem with this application is the dosage and direction of the laser light for accurate removal of the atheroma without damaging the arterial wall. This invention relates to an intravascular catheter for angioplasty using laser light for atheroma ablation and combining it with ultrasonic imaging of the atheroma for guidance of the laser light to obtain precise ablation without damaging the arterial wall. Ultrasonic Doppler blood velocity measurements may also be used to monitor the change in blood flow caused by the increased lumen. The invention also comprises a complete laser beam delivery system for intra-arterial laser angioplasty.
The laser light is delivered to the site using an optical fiber. At the tip of the catheter an ultrasonic transducer is located, and the basic idea of the invention is that the ultrasound transducer and the tip of the optical fiber are mounted so that the directions of the ultrasonic beam and the laser beam are related so that the ultrasound beam can be used to image the atheroma and the arterial wall, and the laser beam can be directed in any selected direction in the image, especially directions where an atheroma is indicated, for controlled ablation of the atheroma. This can be obtained by mounting the ultrasonic transducer and the fiber tip so that the two beam directions coincide, or with different directions of the two beams, the laser beam can be steered to a known direction in the image generated by the ultrasonic beam. Coincident directions of the beams can be obtained by
(i) The fibre tip penetrates the ultrasound transducer with such a small hole that it has negligible effect on the ultrasound beam, and the hole is large enough to feed through the laser light, so that the direction of the laser light and the ultrasound beam substantially coincide. This is schematically illustrated in FIG. 1. PA1 (i) A- or M-mode where range resolution is obtained visualizing the different structures of the atheroma and the arterial wall, as illustrated in FIG. 5 and FIG. 6 respectively. PA1 (ii) The beam direction can be scanned in a plane to generate a 2-dimensional cross section image of the atheroma and the artery, as illustrated in FIG. 7. PA1 (iii) The 2-dimensional scan planes can be moved under position control by moving the catheter along the vessel to generate 3-dimensional images of the atheroma and the arterial wall, as illustrated in FIG. 8. This can be obtained by mounting a longitudinal position sensor, for instance using an optical grating, to the portion of the catheter which is outside the body. The third scan dimension is then obtained by pulling the catheter out of the artery, using the position indication to store 2-dimensional images at defined sections. PA1 a combined laser and ultrasound catheter comprised of PA1 receive circuits adapted to receive and process the backscattered ultrasound for imaging of the tissue structures, and PA1 means for analysing said ultrasound image, either manually or automatically, to determine the presence of atheroma so that said image can be used to direct the laser beam towards the regions in the ultrasound image which have been determined to represent atheroma and determine the intensity and the dosage of the laser beam for accurate ablation of said atheroma. PA1 means for emitting a laser beam in an artery towards an atheroma for ablation of the atheroma, PA1 optical fiber means for feeding laser light from a laser to said emitting means, PA1 an ultrasound transducer for intra-arterial imaging of tissue structures like the atheroma, the vessel wall and surrounding tissue, by emitting a pulsed ultrasound beam towards said tissue structures and also arranged to receive backscattered ultrasound from said tissue structures, and PA1 beam directing means arranged to direct the ultrasound beam towards said tissue structures and also arranged so that the laser beam can be brought into substantially any of the directions the ultrasound beam can assume for imaging, so that the laser beam can be steered towards a portion of the ultrasound image indicating a portion of an atheroma to hit said portion of the atheroma, so that the ultrasound image can be used to guide the laser ablation of the atheroma.
(ii) The laser beam is bent off at an angle by a beam directing arrangement using either a mirror, prism arrangement, bending of the fiber tip, or combination of the three. The ultrasound transducer is mounted at a distance from this arrangement and radiating towards said arrangement which acts as a mirror for the ultrasound beam, so that the ultrasound beam is reflected into the same direction as the laser beam. A typical example of such an arrangement is schematically shown in FIG. 2.
An example of a method by which the beam directions are not coinciding, but interrelated so that the image obtained by the ultrasound beam can be used as a reference for guiding the laser beam, is schematically illustrated in FIG. 3. Here the laser beam is mirrored in the opposite direction to the ultrasound beam, and by rotating the mirror, the laser beam can be aligned to a previous, well known direction of the ultrasound beam.
The ultrasound transducer can be used for pulse echo imaging in the following modes
By imaging we thus mean any kind of presentation of the backscattered ultrasound which relates a portion of the signal to spatial location of the scatterers in the region being sonified. By direction the laser beam along the ultrasonic beam we can obtain a precise observation of both the location of the atheroma to decide where to apply laser light, and continuous monitoring of the effect of the laser light on the atheroma to adaptively determine the energy levels to be applied and when to stop the illumination to avoid damage to the arterial wall. By high energies of the laser light, the ultrasound imaging might be affected by the gas or debris from the ablation of the atheroma, so that it can be advantageous to apply imaging and laser treatment in a time sequence using a spatial interrelation between the beams, so that the laser beam can be directed in a defined direction where an ultrasound image has been obtained. To obtain this, the beam directions do not need to coincide, but they need to be interrelated so that the laser beam can be directed towards a defined part of a previously generated ultrasound image, and the ultrasound beam can be directed towards the place where laser irradiation has occurred, to monitor the effect of the irradiation.
In its broader aspect, the intra-arterial laser angioplasty delivery system according to the invention comprises:
means for emitting a laser beam in an artery towards an atheroma for ablation of the atheroma, PA2 optical fiber means for feeding laser light from a laser to said emitting means, PA2 an ultrasound transducer for intra-arterial imaging of tissue structures like the atheroma, the vessel wall and surrounding tissue, by emitting a pulsed ultrasound beam towards said tissue structures and also arranged to receive backscattered ultrasound from said tissue structures, and PA2 beam directing means arranged to direct the ultrasound beam towards said tissue structures and also arranged so that the laser beam can be brought into for practical purposes any of the directions the ultrasound beam can assume for imaging, so that the laser beam can be steered towards a portion of the ultrasound image indicating a portion of an atheroma for ablation of said portion of the atheroma,
Another aspect of this invention relates to an intra-arterial laser angioplasty catheter comprising: